Targeting RTK Signaling Pathways in Cancer

Shared gene-network signatures between the human heavy metal proteome and neurological disorders and cancer types

In this work, for the first time, the human heavy metal proteome was predicted.

Nuclear membrane-localised NOX4D generates pro-survival ROS in FLT3-ITD-expressing AML

Internal tandem duplication of the juxtamembrane domain of FMS-like tyrosine kinase 3 (FLT3-ITD) is the most prevalent genetic aberration present in 20-30% of acute myeloid leukaemia (AML) cases and is associated with a poor prognosis. FLT3-ITD expressing cells express elevated levels of NADPH oxidase 4 (NOX4)-generated pro-survival hydrogen peroxide (H₂O₂) contributing to increased levels of DNA oxidation and double strand breaks. NOX4 is constitutively active and has been found to have various isoforms expressed at multiple locations within a cell. The purpose of this study was to investigate the expression, localisation and regulation of NOX4 28 kDa splice variant, NOX4D. NOX4D has previously been shown to localise to the nucleus and nucleolus in various cell types and is implicated in the generation of reactive oxygen species (ROS) and DNA damage. Here, we demonstrate that FLT3-ITD expressing-AML patient samples as well as -cell lines express the NOX4D isoform resulting in elevated H₂O₂ levels compared to FLT3-WT expressing cells, as quantified by flow cytometry. Cell fractionation indicated that NOX4D is nuclear membrane-localised in FLT3-ITD expressing cells. Treatment of MV4-11 cells with receptor trafficking inhibitors, tunicamycin and brefeldin A, resulted in deglycosylation of NOX4 and NOX4D. Inhibition of the FLT3 receptor revealed that the FLT3-ITD oncogene is responsible for the production of NOX4D-generated H₂O₂ in AML. We found that inhibition of the PI3K/AKT and STAT5 pathways resulted in down-regulation of NOX4D-generated pro-survival ROS. Taken together these findings indicate that nuclear membrane-localised NOX4D-generated pro-survival H₂O₂ may be contributing to genetic instability in FLT3-ITD expressing AML.

Fibroblast growth factor receptor is a mechanistic link between visceral adiposity and cancer

Epidemiological evidence implicates excess adipose tissue in increasing cancer risk. Despite a steeply rising global prevalence of obesity, how adiposity contributes to transformation (stage a non-tumorigenic cell undergoes to become malignant) is unknown. To determine the factors in adipose tissue that stimulate transformation, we used a novel ex vivo system of visceral adipose tissue (VAT)-condition medium-stimulated epithelial cell growth in soft agar. To extend this system in vivo, we used a murine lipectomy model of ultraviolet light B-induced, VAT-promoted skin tumor formation. We found that VAT from mice and obese human donors stimulated growth in soft agar of non-tumorigenic epithelial cells. The difference in VAT activity was associated with fibroblast growth factor-2 (FGF2) levels. Moreover, human and mouse VAT failed to stimulate growth in soft of agar in cells deficient in FGFR-1 (FGF2 receptor). We also demonstrated that circulating levels of FGF2 were associated with non-melanoma tumor formation in vivo. These data implicate FGF2 as a major factor VAT releases to transform epithelial cells-a novel, potential pathway of VAT-enhanced tumorigenesis. Strategies designed to deplete VAT stores of FGF2 or inhibit FGFR-1 in abdominally obese individuals may be important cancer prevention strategies as well as adjuvant therapies for improving outcomes.

Small molecule inhibitor regorafenib inhibits RET signaling in neuroblastoma cells and effectively suppresses tumor growth in vivo

Neuroblastoma (NB), the most common extracranial pediatric solid tumor, continues to cause significant cancer-related morbidity and mortality in children. Dysregulation of oncogenic receptor tyrosine kinases (RTKs) has been shown to contribute to tumorigenesis in various human cancers and targeting these RTKs has had therapeutic benefit. RET is an RTK which is commonly expressed in NB, and high expression of RET correlates with poor outcomes in patients with NB. Herein we report that RET is required for NB cell proliferation and that the small molecule inhibitor regorafenib (BAY 73-4506) blocks glial cell derived neurotrophic factor (GDNF)-induced RET signaling in NB cells and inhibits NB growth both in vitro and in vivo. We found that regorafenib significantly inhibited cell proliferation and colony formation ability of NB cells. Moreover, regorafenib suppressed tumor growth in both an orthotopic xenograft NB mouse model and a TH-MYCN transgenic NB mouse model. Finally, regorafenib markedly improved the overall survival of TH-MYCN transgenic tumor-bearing mice. In summary, our study suggests that RET is a potential therapeutic target in NB, and that using a novel RET inhibitor, like regorafenib, should be investigated as a therapeutic treatment option for children with NB.

Targeted next-generation sequencing supports epidermoid metaplasia of the esophagus as a precursor to esophageal squamous neoplasia

Esophageal epidermoid metaplasia is a rare condition that involves the proximal-to-middle third of the esophagus. It is sharply demarcated and defined histologically by epithelial hyperplasia, a prominent granular cell layer, and superficial hyperorthokeratosis. In addition, preliminary studies have suggested an association between esophageal epidermoid metaplasia and esophageal squamous neoplasia (squamous dysplasia and esophageal squamous cell carcinoma). To further characterize esophageal epidermoid metaplasia and better define its relationship to squamous neoplasia of the esophagus, we performed targeted next-generation sequencing on uninvolved esophageal squamous mucosa and matching esophageal epidermoid metaplasia specimens from 18 patients. Further, we evaluated both synchronous and metachronous high-grade squamous dysplasia/esophageal squamous cell carcinoma by next-generation sequencing from 5 of the 18 (28%) patients, and compared these findings to corresponding esophageal epidermoid metaplasia specimens. Targeted next-generation sequencing revealed 12 of 18 (67%) esophageal epidermoid metaplasia specimens' harbored alterations in genes often associated with esophageal squamous cell carcinoma. The most frequently mutated genes consisted of TP53 (n=10), PIK3CA (n=2), EGFR (n=2), MYCN (n=1), HRAS (n=1), and the TERT promoter (n=1). Sequencing of synchronous and metachronous high-grade squamous dysplasia/esophageal squamous cell carcinoma identified shared genetic alterations with corresponding esophageal epidermoid metaplasia specimens that suggests a clonal relationship between these entities. In addition, the presence of a TP53 mutation in esophageal epidermoid metaplasia specimens correlated with concurrent or progression to high-grade squamous dysplasia/esophageal squamous cell carcinoma. No genetic alterations were detected in uninvolved esophageal squamous mucosa. On the basis of these findings, we conclude esophageal epidermoid metaplasia is a precursor to in situ and invasive esophageal squamous neoplasia. Further, the detection of TP53 mutations in esophageal epidermoid metaplasia specimens may serve as an early detection biomarker for high-grade squamous dysplasia/esophageal squamous cell carcinoma.

Feedback regulation of RTK signaling in development

Precise regulation of the amplitude and duration of receptor tyrosine kinase (RTK) signaling is critical for the execution of cellular programs and behaviors. Understanding these control mechanisms has important implications for the field of developmental biology, and in recent years, the question of how augmentation or attenuation of RTK signaling via feedback loops modulates development has become of increasing interest. RTK feedback regulation is also important for human disease research; for example, germline mutations in genes that encode RTK signaling pathway components cause numerous human congenital syndromes, and somatic alterations contribute to the pathogenesis of diseases such as cancers. In this review, we survey regulators of RTK signaling that tune receptor activity and intracellular transduction cascades, with a focus on the roles of these genes in the developing embryo. We detail the diverse inhibitory mechanisms utilized by negative feedback regulators that, when lost or perturbed, lead to aberrant increases in RTK signaling. We also discuss recent biochemical and genetic insights into positive regulators of RTK signaling and how these proteins function in tandem with negative regulators to guide embryonic development.

Potential Sabotage of Host Cell Physiology by Apicomplexan Parasites for Their Survival Benefits

Plasmodium, Toxoplasma, Cryptosporidium, Babesia, and Theileria are the major apicomplexan parasites affecting humans or animals worldwide. These pathogens represent an excellent example of host manipulators who can overturn host signaling pathways for their survival. They infect different types of host cells and take charge of the host machinery to gain nutrients and prevent itself from host attack. The mechanisms by which these pathogens modulate the host signaling pathways are well studied for Plasmodium, Toxoplasma, Cryptosporidium, and Theileria, except for limited studies on Babesia. Theileria is a unique pathogen taking into account the way it modulates host cell transformation, resulting in its clonal expansion. These parasites majorly modulate similar host signaling pathways, however, the disease outcome and effect is different among them. In this review, we discuss the approaches of these apicomplexan to manipulate the host–parasite clearance pathways during infection, invasion, survival, and egress.

Lysosome trafficking is necessary for EGF-driven invasion and is regulated by p38 MAPK and Na+/H+ exchangers

Background

Tumor invasion through a basement membrane is one of the earliest steps in metastasis, and growth factors, such as Epidermal Growth Factor (EGF) and Hepatocyte Growth Factor (HGF), stimulate this process in a majority of solid tumors. Basement membrane breakdown is one of the hallmarks of invasion; therefore, tumor cells secrete a variety of proteases to aid in this process, including lysosomal proteases. Previous studies demonstrated that peripheral lysosome distribution coincides with the release of lysosomal cathepsins.

Methods

Immunofluorescence microscopy, western blot, and 2D and 3D cell culture techniques were performed to evaluate the effects of EGF on lysosome trafficking and cell motility and invasion.

Results

EGF-mediated lysosome trafficking, protease secretion, and invasion is regulated by the activity of p38 mitogen activated protein kinase (MAPK) and sodium hydrogen exchangers (NHEs). Interestingly, EGF stimulates anterograde lysosome trafficking through a different mechanism than previously reported for HGF, suggesting that there are redundant signaling pathways that control lysosome positioning and trafficking in tumor cells.

Conclusions

These data suggest that EGF stimulation induces peripheral (anterograde) lysosome trafficking, which is critical for EGF-mediated invasion and protease release, through the activation of p38 MAPK and NHEs. Taken together, this report demonstrates that anterograde lysosome trafficking is necessary for EGF-mediated tumor invasion and begins to characterize the molecular mechanisms required for EGF-stimulated lysosome trafficking.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3660-3) contains supplementary material, which is available to authorized users.

Targeting cellular pathways in glioblastoma multiforme

Glioblastoma multiforme (GBM) is a debilitating disease that is associated with poor prognosis, short median patient survival and a very limited response to therapies. GBM has a very complex pathogenesis that involves mutations and alterations of several key cellular pathways that are involved in cell proliferation, survival, migration and angiogenesis. Therefore, efforts that are directed toward better understanding of GBM pathogenesis are essential to the development of efficient therapies that provide hope and extent patient survival. In this review, we outline the alterations commonly associated with GBM pathogenesis and summarize therapeutic strategies that are aimed at targeting aberrant cellular pathways in GBM.

Anti-pancreatic cancer activity of ONC212 involves the unfolded protein response (UPR) and is reduced by IGF1-R and GRP78/BIP

Pancreatic cancer is chemo-resistant and metastasizes early with an overall five-year survival of ∼8.2%. First-in-class imipridone ONC201 is a small molecule in clinical trials with anti-cancer activity. ONC212, a fluorinated-ONC201 analogue, shows preclinical efficacy in melanoma and hepatocellular-cancer models. We investigated efficacy of ONC201 and ONC212 against pancreatic cancer cell lines (N=16 including 9 PDX-cell lines). We demonstrate ONC212 efficacy in 4 in-vivo models including ONC201-resistant tumors. ONC212 is active in pancreatic cancer as single agent or in combination with 5-fluorouracil, irinotecan, oxaliplatin or RTK inhibitor crizotinib. Based on upregulation of pro-survival IGF1-R in some tumors, we found an active combination of ONC212 with inhibitor AG1024, including in vivo. We show a rationale for targeting pancreatic cancer using ONC212 combined with targeting the unfolded-protein response and ER chaperones such as GRP78/BIP. Our results lay the foundation to test imipridones, anti-cancer agents, in pancreatic cancer, that is refractory to most drugs.

FGF2-mediated attenuation of myofibroblast activation is modulated by distinct MAPK signaling pathways in human dermal fibroblasts

BACKGROUND

Previous human and animal studies have demonstrated the ability of exogenously administered basic fibroblast growth factor (FGF2) to act as an antifibrotic agent in the skin. Though the activity of FGF2 as an anti-scarring agent is well-established for fibrotic skin wounds, the mechanisms by which FGF2 exerts these actions are not entirely understood. Canonical FGF2 signaling proceeds in part via FGFR/MAPK pathways in human dermal fibroblasts, and FGF2 has been described to prevent or reverse the fibroblast-to-myofibroblast transition, which is driven by TGFβ signaling and understood to be an important step in the formation of a fibrotic scar in vivo. Thus, we set out to investigate the antagonistic effects of FGF2 on TGFβ signaling as well as the broader effects of MAPK inhibition on the TGFβ-mediated induction of myofibroblast gene expression.

OBJECTIVE

To better understand the effects of FGF2 signaling pathways on myofibroblastic gene expression and cell phenotypes.

METHODS

Human dermal fibroblasts were cultured in vitro in the presence of FGF2, TGFβ, and/or MAPK inhibitors, and the effects of these agents were investigated by molecular biology techniques including qRT-PCR, immunofluorescence, Western blot, and flow cytometry.

RESULTS

FGF2 inhibited TGFβ-mediated fibroblast activation, resulting in more rapidly proliferating, spindle-shaped cells, compared to the more slowly proliferating, flatter TGFβ-treated cells. Treatment with FGF2 also attenuated TGFβ-mediated increase in expression of myofibroblast markers smooth muscle α-actin, calponin, transgelin, connective tissue growth factor, ED-A fibronectin, and collagen I. FGF2-mediated antagonism of the TGFβ-mediated fibroblast-to-myofibroblast transition was reversed by small molecule inhibition of ERK or JNK, and it was potentiated by inhibition of p38. MAPK inhibition was demonstrated to have qualitatively similar effects even in the absence of exogenous FGF2, and small molecule inhibition of p38 MAPK was sufficient to attenuate TGFβ-mediated fibroblast activation.

CONCLUSIONS

Inhibition of select MAPK signaling pathways can reverse or potentiate anti-fibrotic FGF2 effects on human dermal fibroblasts, as well as exert their effects independently of exogenous FGF2 supplementation.

MLLT3 promotes proliferation of osteosarcoma cells by regulating JNK signaling

Osteosarcoma was the most common malignant tumor derived from bone/soft tissues and afflicted mainly the adolescents. Surgical removing assisted with chemotherapy/radiotherapy was the major therapeutics regardless of high mortality. MLLT3 was one of the most common partners fused with mixed lineage leukemia gene and caused leukemia. But its role in osteosarcoma was not previously reported. In this study, we found that MLLT3 was expressed abundantly in osteosarcoma tissues and cell lines including U-2OS, MG-63, Saos-2 and HOS. And by Kaplan-Meier analysis, MLLT3 expression was shown to be clinically correlated with survival of osteosarcoma patients. The 5-year survival rate was 64.3% for patients with low MLLT3 expression (n=14) while it was 36.4% for patients with high MLLT3 expression (n=11). The difference was significant (p=0.026). When MLLT3 was knocked-down, the proliferation ability decreased about 38% in HOS cells and 46% in MG-63 cells. But the migration as well as the invasive ability was not affected. In addition, the expression level of β-catenin was comparable in HOS cells with/without knockdown of MLLT3. The specific inhibitor LGK-974 against Wnt/β-catenin signaling showed little additive effect with MLLT3 knockdown on growth ability of HOS cells. But the level of c-Jun, BCL-2, Akt and c-Myc was significantly decreased in HOS cells with MLLT3 knockdown, which indicated that MLLT3 may at least partially regulate JNK signaling in HOS cells. In conclusion, we proved MLLT3 as an oncogene in osteosarcoma through partially regulating the JNK signaling pathway. And MLLT3 may be a promising target for treatment of patients with osteosarcoma.

Uncarboxylated Osteocalcin Induces Antitumor Immunity against Mouse Melanoma Cell Growth

Because of the poor response to chemotherapy and radiation therapy, new treatment approaches by immune-based therapy involving activated T cells are required for melanoma. We previously reported that the uncarboxylated form of osteocalcin (GluOC), derived from osteoblasts, potentially suppresses human prostate cancer cell proliferation by direct suppression of cell growth. However, the mechanisms in vivo have not been elucidated. In this study, we found that GluOC suppressed tumor growth of B16 mouse melanoma transplants in C57Bl/6N wild-type mice. Our data demonstrated that GluOC suppressed cell growth by downregulating phosphorylation levels of receptor tyrosine kinases and inducing apoptosis in vitro. Additionally, stimulation of primary mouse splenocytes with concanavalin A, a polyclonal T-cell mitogen, in the presence of GluOC increased T cell proliferation and their interferon-γ production. Taken together, we demonstrate that GluOC exerts multiple antitumor effects not only in vitro, but also in vivo through cellular immunostimulatory effects against B16 mouse melanoma cells.

Genetic association analysis of the RTK/ERK pathway with aggressive prostate cancer highlights the potential role of CCND2 in disease progression

The RTK/ERK signaling pathway has been implicated in prostate cancer progression. However, the genetic relevance of this pathway to aggressive prostate cancer at the SNP level remains undefined. Here we performed a SNP and gene-based association analysis of the RTK/ERK pathway with aggressive prostate cancer in a cohort comprising 956 aggressive and 347 non-aggressive cases. We identified several loci including rs3217869/CCND2 within the pathway shown to be significantly associated with aggressive prostate cancer. Our functional analysis revealed a statistically significant relationship between rs3217869 risk genotype and decreased CCND2 expression levels in a collection of 119 prostate cancer patient samples. Reduced expression of CCND2 promoted cell proliferation and its overexpression inhibited cell growth of prostate cancer. Strikingly, CCND2 downregulation was consistently observed in the advanced prostate cancer in 18 available clinical data sets with a total amount of 1,095 prostate samples. Furthermore, the lower expression levels of CCND2 markedly correlated with prostate tumor progression to high Gleason score and elevated PSA levels, and served as an independent predictor of biochemical relapse and overall survival in a large cohort of prostate cancer patients. Together, we have identified an association of genetic variants and genes in the RTK/ERK pathway with prostate cancer aggressiveness, and highlighted the potential importance of CCND2 in prostate cancer susceptibility and tumor progression to metastasis.

Comprehensive review on cardio-oncology: Role of multimodality imaging

Cancer and cardiovascular disease are the two leading causes of mortality worldwide. Evolving oncologic therapy, including the use of newer targeted agents, has led to an improvement in survival from childhood- and adult-onset cancers. Consequently, there has been a growing realization of cardiotoxic complications related to cancer therapy, with some complications manifesting over months to decades after completion of cancer treatment. This paper reviews cancer therapeutics-related cardiovascular toxicity and its manifestations, multimodality imaging techniques for surveillance and detection of this complication, and the current state of knowledge in this emerging field.

Expression of signaling adaptor proteins predicts poor prognosis in pancreatic ductal adenocarcinoma

Background

Adaptor proteins bridge the gap between cell surface receptors and their downstream signaling elements. The clinicopathological and prognostic values of adaptor proteins remain poorly understood. The purpose of the present study was to explore the expression and prognostic value of three adaptor proteins: GRB2-associated binding protein 2 (GAB2), CRK-like protein (CRKL) and fibroblast growth factor receptor substrate 2 (FRS2) in pancreatic ductal adenocarcinoma (PDAC).

Methods

The expression of GAB2, CRKL, and FRS2 in 77 formalin fixed paraffin embedded (FFPE) samples from 77 PDAC patients, along with three paired fresh PDAC and matched normal tissues from 3 PDAC patients was analyzed by immunohistochemistry and western blot, respectively. The association between the expression of the three proteins and the clinicopathological factors of PDAC was assessed by χ² test. The correlation between the expression levels of the three proteins was analyzed by Spearman rank correlation analyses; Kaplan-Meier survival analyses were also performed.

Results

IHC was successful in 75, 76, and 77 cases for GAB2, CRKL, and FRS2, respectively. Of which, the positive rate of GAB2, CRKL, and FRS2 protein expression was 40.00% (30/75), 53.95% (41/76) and 35.06% (27/77), respectively. The positive rate of GAB2, CRKL and FRS2 co-expression was 16.88% (13/77). Though there was no association between GAB2 expression, CRKL expression, FRS2 expression, GAB2/CRKL/FRS2 co-expression and the clinicopathological parameters of PDAC, positive correlations were observed between the expressions of the three proteins. Further, univariate survival analysis showed that positive expression of GAB2, CRKL and FRS2 and co-expression of GAB2/CRKL/FRS2 of PDAC predicted poor clinical outcomes, and multivariate survival analysis suggested that positive expression of GAB2 and positive co-expression of GAB2/CRKL/FRS2 were independent prognostic factors for disease-free survival (DFS) and overall survival (OS), respectively.

Conclusion

In conclusion, GAB2, CRKL, and FRS2 may be potential prognosticators and therapeutic targets for PDAC patients.

The Function of V-ATPases in Cancer

The vacuolar ATPases (V-ATPases) are a family of proton pumps that couple ATP hydrolysis to proton transport into intracellular compartments and across the plasma membrane. They function in a wide array of normal cellular processes, including membrane traffic, protein processing and degradation, and the coupled transport of small molecules, as well as such physiological processes as urinary acidification and bone resorption. The V-ATPases have also been implicated in a number of disease processes, including viral infection, renal disease, and bone resorption defects. This review is focused on the growing evidence for the important role of V-ATPases in cancer. This includes functions in cellular signaling (particularly Wnt, Notch, and mTOR signaling), cancer cell survival in the highly acidic environment of tumors, aiding the development of drug resistance, as well as crucial roles in tumor cell invasion, migration, and metastasis. Of greatest excitement is evidence that at least some tumors express isoforms of V-ATPase subunits whose disruption is not lethal, leading to the possibility of developing anti-cancer therapeutics that selectively target V-ATPases that function in cancer cells.

Reduction-oxidation pathways involved in cancer development: a systematic review of literature reviews

Oxidative stress results from an imbalance of the reactive oxygen species/reactive nitrogen species (ROS/RNS) production and the oxidants defense system. Extensive research during the last decades has revealed that oxidative stress can mediate cancer initiation and development by leading not only to molecular damage but also to a disruption of reduction-oxidation (redox) signaling. In order to provide a global overview of the redox signaling pathways, which play a role in cancer formation, we conducted a systematic literature search in PubMed and ISI Web of Science and identified 185 relevant reviews published in the last 10 years. The 20 most frequently described pathways were selected to be presented in this systematic review and could be categorized into 3 groups: Intracellular ROS/RNS generating organelles and enzymes, signal transduction cascades kinases/phosphatases and transcription factors. Intracellular ROS/RNS generation organelles are mitochondria, endoplasmic reticulum and peroxisomes. Enzymes, including NOX, COX, LOX and NOS, are the most prominent enzymes generating ROS/RNS. ROS/RNS act as redox messengers of transmembrane receptors and trigger the activation or inhibition of signal transduction kinases/phosphatases, such as the family members of protein tyrosine kinases and protein tyrosine phosphatases. Furthermore, these reactions activate downstream signaling pathways including protein kinase of the MAPK cascade, PI3K and PKC. The kinases and phosphatases regulate the phosphorylation status of transcription factors including APE1/Ref-1, HIF-1α, AP-1, Nrf2, NF-κB, p53, FOXO, STAT, and β-catenin. Finally, we briefly discuss cancer prevention and treatment opportunities, which address redox pathways and further research needs.

Green Tea Catechins for Prostate Cancer Prevention: Present Achievements and Future Challenges

Green tea catechins (GTCs) are a family of chemically related compounds usually classified as antioxidant molecules. Epidemiological evidences, supported by interventional studies, highlighted a more than promising role for GTCs in human prostate cancer (PCa) chemoprevention. In the last decades, many efforts have been made to gain new insights into the mechanism of action of GTCs. Now it is clear that GTCs' anticancer action can no longer be simplistically limited to their direct antioxidant/pro-oxidant properties. Recent contributions to the advancement of knowledge in this field have shown that GTCs specifically interact with cellular targets, including cell surface receptors, lipid rafts, and endoplasmic reticulum, modulate gene expression through direct effect on transcription factors or indirect epigenetic mechanisms, and interfere with intracellular proteostasis at various levels. Many of the effects observed in vitro are dose and cell context dependent and take place at concentrations that cannot be achieved in vivo. Poor intestinal absorption together with an extensive systemic and enteric metabolism influence GTCs' bioavailability through still poorly understood mechanisms. Recent efforts to develop delivery systems that increase GTCs' overall bioavailability, by means of biopolymeric nanoparticles, represent the main way to translate preclinical results in a real clinical scenario for PCa chemoprevention.

Clinical development landscape in GIST: from novel agents that target accessory pathways to revisiting non-targeted therapies

INTRODUCTION

Activating mutations in the genes encoding the tyrosine receptor kinases KIT and platelet-derived growth factor receptor occur in 85%-90% of patients with gastrointestinal stromal tumors (GIST). Although imatinib and other tyrosine kinase inhibitors have revolutionized the treatment of GIST, most patients progress within a few years. Areas covered: Monoclonal antibodies and small-molecule inhibitors targeting specific signaling pathways or proteins associated with resistance to existing treatments are being explored as alternative treatment approaches for GIST. Other alternative approaches include inhibiting more general regulators of protein folding, chromatin packaging, and cell-cycle regulation; nontargeted approaches are also being evaluated in select patient populations. This review summarizes preclinical and clinical data from agents using these accessory pathways. Expert opinion: As we learn more about GIST biology, it is becoming clear that treatment strategies will become more personalized, as reflected by the fact that several trials are enrolling specific subpopulations of patients with GIST. Going forward, researchers should evaluate these new drugs alone or in combination with other types of drugs to better meet patient needs.

Racial disparity in metabolic regulation of cancer

Genetic mutations and metabolic reprogramming are two key hallmarks of cancer, required for proliferation, invasion, and metastasis of the disease. While genetic mutations, whether inherited or acquired, are critical for the initiation of tumor development, metabolic reprogramming is an effector mechanism imperative for adaptational transition during the progression of cancer. Recent findings in the literature emphasize the significance of molecular cross-talk between these two cellular processes in regulating signaling and differentiation of cancer cells. Genome-wide sequencing analyses of cancer genomes have highlighted the association of various genic mutations in predicting cancer risk and survival. Oncogenic mutational frequency is heterogeneously distributed among various cancer types in different populations, resulting in varying susceptibility to cancer risk. In this review, we explore and discuss the role of genetic mutations in metabolic enzymes and metabolic oncoregulators to stratify cancer risk in persons of different racial backgrounds.

Targeting kinase signaling pathways with constrained peptide scaffolds

Kinases are amongst the largest families in the human proteome and serve as critical mediators of a myriad of cell signaling pathways. Since altered kinase activity is implicated in a variety of pathological diseases, kinases have become a prominent class of proteins for targeted inhibition. Although numerous small molecule and antibody-based inhibitors have already received clinical approval, several challenges may still exist with these strategies including resistance, target selection, inhibitor potency and in vivo activity profiles. Constrained peptide inhibitors have emerged as an alternative strategy for kinase inhibition. Distinct from small molecule inhibitors, peptides can provide a large binding surface area that allows them to bind shallow protein surfaces rather than defined pockets within the target protein structure. By including chemical constraints within the peptide sequence, additional benefits can be bestowed onto the peptide scaffold such as improved target affinity and target selectivity, cell permeability and proteolytic resistance. In this review, we highlight examples of diverse chemistries that are being employed to constrain kinase-targeting peptide scaffolds and highlight their application to modulate kinase signaling as well as their potential clinical implications.

Non-canonical Activation of Receptor Tyrosine Kinases in Cancer Progression

Receptor tyrosine kinases (RTKs) are known to be key regulators of cancer cell proliferation, migration, invasion and metastatic spread. Ligand-binding to the extracellular domain triggers canonical activation of the intracellular tyrosine kinase domain. In contrast, it has become evident that RTKs are also regulated by non-canonical tyrosine kinase-independent mechanisms via phosphorylation of their serine/threonine residues. In this review, I mainly introduce our recent findings on the non-canonical regulation of epidermal growth factor receptor (EGFR), ErbB2 and erythropoietin-producing hepatocellular receptor A2 (EphA2), and discuss the roles of non-canonical activation of RTKs in cancer progression and resistance to targeted cancer agents. Further characterization of non-canonical regulation will contribute to the development of new target cancer therapies.

The Glycosyltransferase ST6Gal-I Protects Tumor Cells against Serum Growth Factor Withdrawal by Enhancing Survival Signaling and Proliferative Potential

A hallmark of cancer cells is the ability to survive and proliferate when challenged with stressors such as growth factor insufficiency. In this study, we report a novel glycosylation-dependent mechanism that protects tumor cells from serum growth factor withdrawal. Our results suggest that the β-galactoside α-2,6-sialyltransferase 1 (ST6Gal-I) sialyltransferase, which is up-regulated in numerous cancers, promotes the survival of serum-starved cells. Using ovarian and pancreatic cancer cell models with ST6Gal-I overexpression or knockdown, we find that serum-starved cells with high ST6Gal-I levels exhibit increased activation of prosurvival signaling molecules, including pAkt, p-p70S6K, and pNFκB. Correspondingly, ST6Gal-I activity augments the expression of tumor-promoting pNFκB transcriptional targets such as IL-6, IL-8, and the apoptosis inhibitor cIAP2. ST6Gal-I also potentiates expression of the cell cycle regulator cyclin D2, leading to increased phosphorylation and inactivation of the cell cycle inhibitor pRb. Consistent with these results, serum-starved cells with high ST6Gal-I expression maintain a greater number of S phase cells compared with low ST6Gal-I expressors, reflecting enhanced proliferation. Finally, selective enrichment in clonal variants with high ST6Gal-I expression is observed upon prolonged serum deprivation, supporting the concept that ST6Gal-I confers a survival advantage. Collectively, these results implicate a functional role for ST6Gal-I in fostering tumor cell survival within the serum-depleted tumor microenvironment.

Small GTPase Rab8a-recruited Phosphatidylinositol 3-Kinase γ Regulates Signaling and Cytokine Outputs from Endosomal Toll-like Receptors

LPS-mediated activation of Toll-like receptor 4 (TLR4) in macrophages results in the coordinated release of proinflammatory cytokines, followed by regulatory mediators, to ensure that this potentially destructive pathway is tightly regulated. We showed previously that Rab8a recruits PI3Kγ for Akt-dependent signaling during TLR4 activation to limit the production of the proinflammatory cytokines IL-6 and IL-12p40 while enhancing the release of the regulatory/anti-inflammatory cytokine IL-10. Here we broaden the array of immune receptors controlled by Rab8a-PI3Kγ and further define the Rab-mediated membrane domains required for signaling. With CRISPR/Cas9-mediated gene editing to stably knock out and recover Rab8a in macrophage cell lines, we match Akt signaling profiles with cytokine outputs, confirming that Rab8a is a novel regulator of the Akt/mammalian target of rapamycin (mTOR) pathway downstream of multiple TLRs. Upon developing a Rab8a activation assay, we show that TLR3 and 9 agonists also activate Rab8a. Live-cell imaging reveals that Rab8a is first recruited to the plasma membrane and dorsal ruffles, but it is retained during collapse of ruffles to form macropinosomes enriched for phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P₃) and phosphatidylinositol 3,4-bisphosphate (PI(3,4)P₂), suggesting that the macropinosome is the location where Rab8a is active. We pinpoint macropinosomes as the sites for Rab8-mediated biasing of inflammatory signaling responses via inducible production of anti-inflammatory cytokines. Thus, Rab8a and PI3Kγ are positioned in multiple TLR pathways, and this signaling axis may serve as a pharmacologically tractable target during infection and inflammation.

Development of crizotinib, a rationally designed tyrosine kinase inhibitor for non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the number one cause of global mortality. Despite aggressive treatment, the prognosis is dismal. Patients with advanced NSCLC have a median survival of 4 months from the time of diagnosis. Fortunately, molecularly based approaches to drug discovery have yielded a tyrosine kinase inhibitor, crizotinib, which significantly prolongs median progression-free survival in a subset of patients. Although initial clinical trial results demonstrate crizotinib has a promising role to play in NSCLC treatment, development of resistance leaves much to be elucidated about how to effectively combat this deadly disease. In this review, we follow the discovery and development of crizotinib from bench to bedside and provide an example of successful bottom-up drug design. Then, we explore the clinical trial results that fast-tracked its eventual use as a frontline therapy for sensitive NSCLC patients and the development of resistance. Lastly, we discuss the potential for future uses of crizotinib both within and beyond NSCLC.

Discovering novel 7-azaindole-based series as potent AXL kinase inhibitors

AXL is a receptor tyrosine kinase that plays a key role in tumor growth and proliferation. The scientific community has validated AXL as therapeutic target in the treatment of cancers for several years now, and several AXL inhibitors have been developed but none of them are approved. In this context, we started to design new kinase inhibitors targeting AXL from the 7-azaindole scaffold well known to interact with the ATP binding site of the kinase. Focused screening and chemical diversification around 7-azaindole scaffold were developed, based on modeling studies and medicinal chemistry rational, leading to the discovery of a new family of hits with potent inhibitory activity against AXL.

Evaluating the mechanistic evidence and key data gaps in assessing the potential carcinogenicity of carbon nanotubes and nanofibers in humans

In an evaluation of carbon nanotubes (CNTs) for the IARC Monograph 111, the Mechanisms Subgroup was tasked with assessing the strength of evidence on the potential carcinogenicity of CNTs in humans. The mechanistic evidence was considered to be not strong enough to alter the evaluations based on the animal data. In this paper, we provide an extended, in-depth examination of the in vivo and in vitro experimental studies according to current hypotheses on the carcinogenicity of inhaled particles and fibers. We cite additional studies of CNTs that were not available at the time of the IARC meeting in October 2014, and extend our evaluation to include carbon nanofibers (CNFs). Finally, we identify key data gaps and suggest research needs to reduce uncertainty. The focus of this review is on the cancer risk to workers exposed to airborne CNT or CNF during the production and use of these materials. The findings of this review, in general, affirm those of the original evaluation on the inadequate or limited evidence of carcinogenicity for most types of CNTs and CNFs at this time, and possible carcinogenicity of one type of CNT (MWCNT-7). The key evidence gaps to be filled by research include: investigation of possible associations between in vitro and early-stage in vivo events that may be predictive of lung cancer or mesothelioma, and systematic analysis of dose-response relationships across materials, including evaluation of the influence of physico-chemical properties and experimental factors on the observation of nonmalignant and malignant endpoints.

Mitogenic signaling pathways in the liver of growth hormone (GH)-overexpressing mice during the growth period

Growth hormone (GH) is a pleiotropic hormone that triggers STATs, ERK1/2 and Akt signaling, related to cell growth and proliferation. Transgenic mice overexpressing GH present increased body size, with a disproportionate liver enlargement due to hypertrophy and hyperplasia of the hepatocytes. We had described enhanced mitogenic signaling in liver of young adult transgenic mice. We now evaluate the activation of these signaling cascades during the growth period and relate them to the morphological alterations found. Signaling mediators, cell cycle regulators and transcription factors involved in cellular growth in the liver of GH-overexpressing growing mice were assessed by immunoblotting, RT-qPCR and immunohistochemistry. Hepatocyte enlargement can be seen as early as 2-weeks of age in GH-overexpressing animals, although it is more pronounced in young adults. Levels of cell cycle mediators PCNA and cyclin D1, and transcription factor c-Jun increase with age in transgenic mice with no changes in normal mice, whereas c-Myc levels are higher in 2-week-old transgenic animals and cyclin E levels decline with age for both genotypes. STAT3, Akt and GSK3 present higher activation in the adult transgenic mice than in the growing animals, while for c-Src and mTOR, phosphorylation in GH-overexpressing mice is higher than in control siblings at 4 and 9 weeks of age. No significant changes are observed for ERK1/2, neither by age or genotype. Thus, the majority of the mitogenic signaling pathways are gradually up-regulated in the liver of GH-transgenic mice, giving rise to the hepatic morphological changes these mice exhibit.

MEK inhibitors against MET-amplified non-small cell lung cancer

Several receptor tyrosine kinases (RTKs) including EGFR, ALK, and MET have been identified as therapeutic targets in non-small cell lung cancer (NSCLC). Among the downstream pathways of RTKs, the MAPK pathway is particularly important for cancer cell proliferation, differentiation, and survival. In this study, the effects of MEK inhibitors (trametinib and PD0325901) in several NSCLC cell lines with driver gene alterations, especially RTK genes, were tested in vitro using an MTT assay, and a wide range of sensitivities was found. In particular, all the EGFR-mutated cell lines were resistant to MEK inhibitors, whereas all the MET-amplified cell lines were sensitive. A bioinformatics technique and western blot analyses showed that the PI3K/AKT pathway is more activated in EGFR-mutated NSCLC than in MET-amplified NSCLC, and a PI3K inhibitor enhanced the sensitivity to trametinib in the EGFR-mutated cell lines, suggesting that this pathway is associated with resistance to MEK inhibitors. Although the HCC827 cell line (EGFR mutation) was resistant to MEK inhibitors, the HCC827CNXR cell line, whose driver gene shifts from EGFR to MET, exhibited enhanced sensitivity to MEK inhibitors, indicating the biological importance of the MAPK pathway for MET-amplified NCSLC. Furthermore, a synergistic effect of crizotinib (a MET inhibitor) and trametinib was observed in MET-amplified NCLC cell lines. Our findings indicate that the MAPK pathway is biologically important for MET-amplified NSCLC and strongly encourage the development of combination therapy with a MET inhibitor and a MEK inhibitor against MET-amplified NSCLC.

Wnt Drug Discovery: Weaving Through the Screens, Patents and Clinical Trials

The Wnt signaling pathway is intricately involved in many aspects of development and is the root cause of an increasing number of diseases. For example, colorectal cancer is the second leading cause of death in the industrialized world and aberration of Wnt signaling within the colonic stem cell is the cause of more than 90% of these cancers. Despite our advances in successfully targeting other pathways, such as Human Epidermal Growth Factor Receptor 2 (HER2), there are no clinically relevant therapies available for Wnt-related diseases. Here, we investigated where research activities are focused with respect to Wnt signaling modulators by searching the United States Patent and Trade Office (USPTO) for patents and patent applications related to Wnt modulators and compared this to clinical trials focusing on Wnt modulation. We found that while the transition of intellectual property surrounding the Wnt ligand-receptor interface to clinical trials is robust, this is not true for specific inhibitors of β-catenin, which is constitutively active in many cancers. Considering the ubiquitous use of the synthetic T-cell Factor/Lymphoid Enhancer Factor (TCF/Lef) reporter system and its success in identifying novel modulators in vitro, we speculate that this model of drug discovery does not capture the complexity of in vivo Wnt signaling that may be required if we are to successfully target the Wnt pathway in the clinic. Notwithstanding, increasingly more complex models are being developed, which may not be high throughput, but more pragmatic in our pursuit to control Wnt signaling.

Guidance of Signaling Activations by Cadherins and Integrins in Epithelial Ovarian Cancer Cells

Epithelial ovarian cancer (EOC) is the deadliest tumor among gynecological cancer in the industrialized countries. The EOC incidence and mortality have remained unchanged over the last 30 years, despite the progress in diagnosis and treatment. In order to develop novel and more effective therapeutic approaches, the molecular mechanisms involved in EOC progression have been thoroughly investigated in the last few decades. At the late stage, peritoneal metastases originate from the attachment of small clusters of cancer cells that shed from the primary site and carried by the ascites adhere to the abdominal peritoneum or omentum. This behavior suggests that cell–cell or cell–matrix adhesion mechanisms regulate EOC growth and dissemination. Complex downstream signalings, which might be influenced by functional cross-talk between adhesion molecules and co-expressed and activated signaling proteins, can affect the proliferation/survival and the migration/invasion of EOC cells. This review aimed to define the impact of the mechanisms of cell–cell, through cadherins, and cell–extracellular matrix adhesion, through integrins, on the signaling cascades induced by membrane receptors and cytoplasmic proteins known to have a role in the proliferation, migration and invasion of EOC cells. Finally, some novel approaches using peptidomimetic ligands to cadherin and integrins are summarized.

Rare SNPs in receptor tyrosine kinases are negative outcome predictors in multiple myeloma

Multiple myeloma (MM) is a plasma cell disorder that is characterized by a great genetic heterogeneity. Recent next generation sequencing studies revealed an accumulation of tumor-associated mutations in receptor tyrosine kinases (RTKs) which may also contribute to the activation of survival pathways in MM. To investigate the clinical role of RTK-mutations in MM, we deep-sequenced the coding DNA-sequence of EGFR, EPHA2, ERBB3, IGF1R, NTRK1 and NTRK2 which were previously found to be mutated in MM, in 75 uniformly treated MM patients of the "Deutsche Studiengruppe Multiples Myelom". Subsequently, we correlated the detected mutations with common cytogenetic alterations and clinical parameters. We identified 11 novel non-synonymous SNVs or rare patient-specific SNPs, not listed in the SNP databases 1000 genomes and dbSNP, in 10 primary MM cases. The mutations predominantly affected the tyrosine-kinase and ligand-binding domains and no correlation with cytogenetic parameters was found. Interestingly, however, patients with RTK-mutations, specifically those with rare patient-specific SNPs, showed a significantly lower overall, event-free and progression-free survival. This indicates that RTK SNVs and rare patient-specific RTK SNPs are of prognostic relevance and suggests that MM patients with RTK-mutations could potentially profit from treatment with RTK-inhibitors.